How many watts or heart rate is right for 90 km? Why overpacing in the first 30 minutes kills the half marathon after — and how to avoid it.
"How hard can I actually ride the 90 km without wrecking the run afterward?" The honest answer: less hard than it feels like you should. Most age-group half-distance races aren't lost in the half marathon — they're lost in the first 30 to 45 minutes on the bike. Ride too aggressively there and the damage is done long before the first kilometer of the run even starts.
The benchmark coaches work with: a normalized power of roughly 70 to 78% of your bike FTP across the full 90 km — FTP stands for "Functional Threshold Power," the output you can sustain for about an hour straight. For first-timers or weaker runners the safe range sits closer to 70–72%, while very run-strong, experienced athletes can push to 80–85%. As a rough rule of thumb: if your power sits at 82% instead of 74% FTP after 20 minutes, the damage to your run is usually already done.
No power meter? Translate it into heart rate or perceived effort instead: you should still be able to speak in full sentences on the bike, not just single words.
Calculate a concrete watt or heart-rate zone before the race — 70–78% of your FTP as a normalized-power target. Write the number on your handlebars or watch. A target you invent mid-race is almost always too ambitious.
This is exactly where the most common mistake happens: adrenaline, fresh legs and the feeling "I could go much faster" tempt you to ride well above your target zone. Ride the first kilometers toward the low end of your zone, even if it feels too slow.
Between kilometer 20 and 70, discipline is what counts: steady output rather than surging and recovering. Use climbs for brief extra output and descents for deliberate recovery — as long as the average stays in your target zone.
In the final kilometers the mental shift begins: raise cadence slightly, spin easier gears, so your legs aren't stuck entirely in "bike mode." This noticeably eases the transition into running.
Compare your actual normalized power to your target and to your run time afterward. Were you too hard and did the run fall apart? That's the most important learning curve for your next race.
Pacing the bike too hard doesn't just hurt your run — it can trigger circulatory problems in transition: dizziness, nausea or cramps right after dismounting are common warning signs. Dismount more slowly if you notice these symptoms and ease deliberately into the first meters of the run.
Keep drinking and eating steadily throughout the bike leg even while you focus on pacing — under-fueling makes the consequences of overpacing even worse.
Use a simple self-check in the first 10 minutes of the bike: can you still speak a full sentence without effort? If not, you're riding too hard — before your watch or power meter even tells you.
A coaching trick: on a hilly course, don't set a watt target for every single climb — set a total target for the whole course instead. That way you avoid blowing your zone on every hill and still land on plan at the finish.
The usual target range is 70–78% of your FTP as normalized power across the full 90 km. First-timers and weaker runners should stay toward the lower end; very run-strong, experienced athletes can push to 80–85%.
Because the most common mistake happens in the first 30–45 minutes: riding too hard on adrenaline and fresh legs. That early mistake only shows its effect later — usually in the half marathon, when it's too late to fix.
Use the talk-test rule: as long as you can still speak full sentences on the bike, you're in a sustainable zone. Once speaking becomes an effort, you're riding too hard for the remaining distance.
In moderation, yes, but without blowing your overall zone for the course. Use climbs for controlled extra effort and descents for deliberate recovery — in the end the average matters, not the peaks.
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